1. Field of the Invention
The present invention relates to metal silicate films. In particular, the invention concerns methods for forming metal silicate films by atomic layer deposition (ALD).
2. Description of the Related Art
The integration level of components in integrated circuits is increasing, which rapidly places a demand for a decrease of the size of integrated circuit (IC) components and interconnects. Design rules are setting the feature sizes to ≦0.2 μm, making complete film coverage on deep bottoms and vias difficult to obtain using traditional methods. Additionally, with decreasing feature sizes, quantum mechanical tunneling (“tunneling”) leads to leakage current, i.e., current leaking out of device features (e.g., across gate oxides), which adversely affects device performance. For this reason, substantially thin SiO2 films are unreliable as gate dielectrics (gate oxides), for example, in MOSFET (metal-oxide-semiconductor field-effect transistor) devices. Thus, a dielectric material with a high dielectric constant (“high-k dielectric”) is desirable.
High-k dielectric materials should preferably be able to be deposited on silicon surfaces and remain stable under thermal annealing processes. In gate dielectric applications, electrically active defects should be minimized or prevented from forming at interfaces between silicon wafers and high-k dielectrics. In memory applications, such as in dynamic random access memory (DRAM) applications, the structure of the dielectric should preferably be substantially stable under high activation temperatures. It has been found that mixing silicon oxide (SiOx, where ‘x’=1 or 2) with a metal oxide forms stable metal silicates that can be used as high-k dielectrics with desirable properties.
Hafnium silicate (HfSiOx) and Zirconium silicate (ZrSiOx) have been used to replace silicon oxide in some applications, such as complementary metal oxide semiconductor (CMOS) applications, because they can offer excellent thermal stability and device performance in integrated circuits with device features sizes of about 65 nanometers (nm) or less. However, with decreasing features sizes, it has become increasingly difficult to deposit hafnium silicate films with compositional and thickness uniformities suited for current and future generation of ICs.
A problem with prior art ALD methods is that halide-based source chemicals (e.g., MX4 and SiY4, wherein “M” is a metal and “X” and “Y” are halides) leave halogen atoms in the metal silicate film, leading to substantially high “fixed charge” concentrations that can degrade the performance of electrical devices, such as CMOS and DRAM devices. On the other hand, purely organic source chemicals lead to carbon impurities in the film, which behave as charge centers. At high concentrations, carbon impurities promote leakage currents that lead to increased power consumption in CMOS devices and decreased storage capabilities in DRAM devices.
Methods that have previously been employed in ameliorating the problems with metal silicate films formed using exclusively halide or organic-based source chemicals typically involve annealing and/or oxidizing the films. These methods can lead to substantial increases in processing costs and may promote oxidation of the interface between the metal silicate film and the underlying substrate, thus leading to poor film quality and poor device performance.